Nurse Shark

Nurse Shark

Cartilaginous Fish

SCIENTIFIC CLASSIFICATION

COMMON NAME:

nurse shark

KINGDOM:

Animalia

PHYLUM:

Chordata

CLASS:

Chondrichthyes

ORDER:

Orectolobiformes

FAMILY:

Ginglymostomatidae

GENUS SPECIES:

Ginglymostomacirratum

FAST FACTS

DESCRIPTION:

Body is yellow-brown to gray-brown, with or without small dark spots and obscure dorsal saddle markings. Mouth is set forward of eyes and is relatively high up on the head - maintaining a more forward position. Noticeable barbells are present, along with nasoral grooves (though there are no perinasal grooves). Spiracles are minute. Dorsal fins are broad and rounded, with the first dorsal being considerably larger than the second. Dorsal fins are set relatively far back along the ventral surface. The upper lobe of the caudal fin is considerably longer than the lower lobe. The caudal fin itself comprises roughly one quarter of the overall body length.

MALE

External claspers located on the far underside of the body - forward of the caudal fin - distinguish males.

SIZE:

300 cm (10.0 ft) avg; 430 cm (14.1 ft) max

WEIGHT:

110 kg (242.5 lbs) max

DIET:

Nurse sharks primarily feed on benthic invertebrates (i.e. spiny lobsters, shrimps, crabs, sea urchins, squids, octopuses, marine snails and bivalves) and benthic fish (i.e. sea catfishes, mullets, puffers and stingrays). Though algal species are occasionally found within their stomachs, nurse sharks are not considered omnivores. Rather, the algal material is likely consumed as a consequence to the shark's pursuit of benthic prey.

The smallish mouth and large bellows-like pharynx of the nurse shark allow this species to inhale prey items with tremendous force and speed. This powerful suction feeding mechanism combined with the species' nocturnal activity pattern, may allow the nurse shark to successfully prey upon small, active diurnal fish species which are at rest during the overnight hours. (During the day, such active, mid-water species would be beyond the predatory capabilities of the nurse shark.)

Nurse sharks are known to successfully feed on large, heavy shelled marine snails (i.e. conches) by flipping the shell over, exposing the vulnerable apeture. Using their teeth and suction, the shark then extracts the snail from its shell altogether.

GESTATION:

Nurse sharks exhibit ovoviviparous reproduction in which yolk sacks primarily sustain the intrauterine development of the young. Within the waters adjacent to Florida, birthing typically occurs in late spring and early summer months.

CLUTCH SIZE

Litters are comprised of 21-28 intrauterine eggs or young (distinction of "eggs" versus "young" is dependent on the time of sampling within the intrauterine development process).

SEXUAL MATURITY:

MALE

Approximately 225 cm

FEMALE

230-240 cm

LIFE SPAN:

Approximately 25 years in zoological facilities

RANGE:

Western Atlantic: shallow waters from Rhode Island to Brazil, including the Caribbean basin and Gulf of Mexico
Eastern Atlantic: tropical West Africa to the Cape Verde Islands
Eastern Pacific: southern Baja California to Peru

HABITAT:

The nurse shark is a common large inshore shark (primarily benthic) inhabiting the continental and insular shelves throughout tropical and subtropical waters within its range. They are often observed at depths of a meter or less within the intertidal zone, though they are known to range down to depths of at least 12 meters. This species is often found along reef sites, within mangrove channels, and on sand or seagrass flats.

POPULATION:

GLOBAL

While global population figures are unknown, nurse sharks are common in shallow waters within their range.

STATUS:

IUCN

Not listed

CITES

Not listed

USFWS

Not listed

FUN FACTS

1.

One of the distinguishing features of nurse sharks are their barbells - fleshy appendages which hang below their nostrils and, in part, provide a sense of touch which assists in the location of prey along the bottom.

2.

Unlike most sharks, which require constant motion to move water over their gills and maintain a sufficient internal blood pressure, the nurse shark often remains motionless along the bottom - actively pumping water over its gills through the continual opening and closing of its mouth.

3.

Though documented attacks - some of which have resulted in painful wounds - are associated with this species, nurse sharks are generally considered a docile shark species. Virtually every tallied attack has been provoked. The nurse shark's tendency to lay motionless on the bottom seems to lull divers into a false sense of security - occasionally leading to the poking, prodding, or pulling of a wild nurse shark. Such human behavior can lead to defensive actions on the part of the shark…and ending in an additional "attack" statistic.

4.

Nurse sharks do well in zoological settings. They have been documented living to twenty-five years of age within public aquaria.

5.

In learning experiments, nurse sharks have shown themselves capable of being trained to swim to a handler to receive food.

ECOLOGY AND CONSERVATION

The nurse shark is privately and commercially harvested for its thick, armor-like hide, which is processed into an exceptionally good leather. They are also targeted for consumption, whether it be fresh or salted. Additionally they are harvested for their liver oil and for use as fishmeal.

Nurse sharks have proven to be a hardy, adapatable species - capable of surviving a relatively broad range of temperatures and dissolved oxygen levels.

In 1993, the U.S. National Marine Fisheries Service (NMFS) established a management plan designed to protect 39 shark species found in Atlantic and Gulf of Mexico waters. The purview of this plan encompassed the Exclusive Economic Zone (EEZ) - the area extending from state waters out to 200 miles offshore. This NMFS plan aims at stabilizing shark populations through the reduction of commercial and recreational fishing pressures via licensing and take quotas. The nurse shark is one of the 39 species covered in this plan.

BIBLIOGRAPHY

Allen, Thomas B., The Shark Almanac. The Lyons Press, 1999.

Compagno, Leonard J.V., FAO Species Catalog, Vol. 4 Sharks of the World. United Nations Development Programme, Food and Agriculture Organization of the United Nations, Rome, 1984.